In an LTE network, the UE is responsible for, among other things, measuring/estimating signal strength in its cell (or primary cell) and neighboring cells (or secondary cells), and reporting such measurements to the network. One such measurement is the Reference Signal Received Power (RSRP), which measures the power of a cell's received reference signals (RSs). More specifically, the UE measures the cell-specific RSs (CRSs) for that cell. FIG. 1 shows the distribution of CRSs within a subframe depending on the number of antennas being used in a case of a normal cyclic prefix (CP). An LTE Frequency Division Duplexing (FDD) subframe is 1/10th of a frame and includes two slots, each of which has 7 symbols (labelled 0 through 6) and 12 sub-carriers. As shown in FIG. 1, the CRSs are always in symbol 0 (the first) and symbol 4 (the fifth) of every slot and, within a symbol, the CRSs are always separated by 6 subcarriers.
The UE could be provided with the list of cells to measure (or neighbor list) by the network or by a cell searcher which plays the role of finding/identifying LTE cells. In the latter case, however, sometimes the list of cells include a ghost cell, which is not a cell at all, but rather the false identification of a cell where there isn't one. Such ghost cells degrade performance system-wide and inevitably waste resources.
More specifically, field tests have shown that if a UE sends a measurement report that includes ghost cells to the network, the UE will suffer performance degradation (such as radio link failure). An LTE feature may include using the UE to build and correct the list of cells. For example, the network relies upon the UE to report any cells it has detected which are not on the network's neighbor list. If the UE reports a ghost cell in such a scenario, it may trigger the network to initiate the Automatic Neighbor Relation (ANR) procedure, which is destined to fail (being initiated by a non-existent cell) and may further cause a radio link failure.